In a mobile communication, data communication such as transmission/reception of mails using a mobile station and accesses to the Internet is performed between the mobile station and a contents server as an access destination, by using Internet Protocol (hereinafter called IP) packets. In order to realize such data communication, it is known that IP packet communication is performed between a mobile station and a packet data serving node (hereinafter called PDSN (Packet Data Serving Node)) by using Point to Point Protocol (hereinafter called PPP) standardized by RFC1661 (refer to 3GPP2 X. S0011-C cdma2000 Wireless IP network Standard).
PPP is used for data communication between devices directly interconnected by a WAN line such as dial-up connection and ISDN and between a mobile radio station and a PDSN in a mobile communication system. The status of each device is set by transmission/reception of user authentication, protocols, addresses, a compression and error correction method and the like to be used, between devices by using various PPP packets prescribed in RFC1661, to thereby allow data transfer using not only IP packets but also various protocols. When a mobile station sends an IP packet to a contents server, the mobile station generates a PPP packet by adding a PPP header to the IP packet to transmit data to PDSN via a provider network. PDSN removes the PPP header of the PPP packet to extract the IP packet, and thereafter transfers the IP packet to an access destination contents server via a public network.
Fundamental operations regarding PPP connection/disconnection between a communication terminal device and PDSN include a link establishment phase, a user authentication phase, a network-layer protocol phase and a link termination phase. The link establishment (hereinafter called Link Control Protocol (LCP)) phase establishes a data link by using LCP when a physical line connection is completed, and decides a data size, presence/absence of compression, a rate and the like. The user authentication phase performs user authentication such as permission/rejection of a partner access authority. The network-layer protocol (hereinafter called Network Control Protocol (NCP)) phase is a phase for selecting an upper protocol and setting network address assignment by using NCP to release a network. The link termination phase is a phase for terminating a PPP link by using LCP.
More detailed description will be made. PPP is constituted of two protocols: LCP and NCP. LCP is a protocol for controlling link establishment and user authentication in a physical line connection state. NCP is a protocol for assigning addresses determined by a layer 3 protocol (network layer protocol), and has a function of assigning, for example, an IP address if the network layer uses IP. NCP designates a type of a layer 3 protocol in a protocol field of an NCP packet (one kind of a PPP packet) to thereby decide which one of a plurality of layer 3 protocols is to be used. For example, if IPv4 is to be used which is prescribed in RFC791 (Internet Protocol), 8021 in hexadecimal notation is set to the protocol field. IPv4 stipulates a selection of a route for sending, to a transfer partner, a data packet (data such as File Transfer Protocol (FTP) for file transfer and Transmission Control Protocol (TCP) for high reliability communication). With this route selection, IP addresses of a 32-bit numerical number are used, so that about four billion and two hundred million addresses can be distinguished at a maximum. If IPv6 is to be used which is prescribed in RFC2460 (Internet Protocol, Version 6), 8057 in hexadecimal notation is set to the protocol field. IPv6 can distinguish an IP address from a 128-bit numerical number. This protocol has been developed due to grave misgivings about exhaustion of address resources to be caused by recent rapid spread of the Internet, and is expected to be applied to future Internet communication.
As prescribed in RFC1661 for PPP connection operation between a terminal and PDSN, the LCP phase is first executed, and if a data link is established, an authentication process is executed in the authentication phase. After the authentication is completed, the NCP phase is effected for decision of a protocol to be used, selection (designation) of an IP address and the like.
In a communication system in which PDSN is equipped with both IPv4 and IPv6 protocols and a terminal is equipped with only an IPv6 protocol, the NCP phase is effected after the LCP phase process and authentication process are completed between a mobile station and PDSN. According to the prescription of RFC1661, the NCP phase is effected for all protocols equipped in PDSN. This operation is performed in the following manner.
Although the terminal is equipped with only the IPv6 protocol, PDSN is equipped with both the IPv4 and IPv6 protocols. Therefore, PDSN executes the NCP phase for both the protocols and transmits an IPCP Configure Request packet for IPv4 and an IPv6CP Configure Request packet for IPv6, to the terminal. The terminal returns an LCP Protocol Reject packet representative of non-equipment in response to the received IPCP Configure Request Packet. Since the terminal is equipped with the IPv6 protocol, the terminal transmits an IPv6CP Configure Request packet to PDSN in parallel to the operation of PDSN.
Upon reception of the LCP Protocol Reject packet from the terminal, PDSN decides termination of the NCP phase for IPv4 and terminates NCP negotiation for the rejected protocol. In response to the IPv6CP Configure Request packet received from the terminal, PDSN transmits an IPv6CP Configure Ack packet representative of connection permission, to the terminal. When this packet is received, connection preparation at the terminal is completed. When the IPv6CP Configure Ack packet representative of connection permission is received from the terminal in response to the IPv6CP Configure Request packet transmitted from PDSN, connection preparation at PDSN is also completed. In this manner, PPP connection allowing IPv6 network communication is completed.
As described above, in the connection operation via a network using PPP, a terminal requiring connection issues a call to PDSN to effect negotiation for connection establishment and user authentication under LCP, as disclosed in RFC1661. Thereafter, PDSN establishes PPP connection under NCP by negotiations with types of all protocols equipped in PDSN.